Metal-containing zeolite catalyst, preparation thereof and use for hydrocarbon conversion

ABSTRACT

There is provided a zeolite bound zeolite catalyst which does not contain significant amounts of non-zeolitic binder and a process for converting hydrocarbons utilizing the zeolite bound zeolite catalyst. The catalyst comprises first zeolite, crystals, a binder comprising second zeolite crystals and a hydrogenation/dehydrogenation metal. The zeolite bound zeolite catalyst is prepared by converting the silica binder of a silica bound aggregate containing the first crystals of said first zeolite and at least a portion of the hydrogenation/dehydrogenation metal to said second zeolite. The zeolite bound zeolite catalyst has excellent performance when used in hydrocarbon conversion processes such as naphtha reforming and xylenes isomerization/ethylbenzene conversion.

This application claims benefit of provisional application 60/018,583,filed May 29, 1996.

FIELD OF THE INVENTION

This invention relates to a method of preparing zeolite bound zeolitecatalysts having enhanced hydrogenation/dehydrogenation metaldispersion, the catalyst itself, and the use of the catalyst inhydrocarbon conversion processes.

BACKGROUND OF THE INVENTION

Crystalline microporous molecular sieves, both natural and synthetic,have been demonstrated to have catalytic properties for various types ofhydrocarbon conversion processes. In addition, the crystallinemicroporous molecular sieves have been used as adsorbents and catalystcarriers for various types of hydrocarbon conversion processes, andother applications. These molecular sieves are ordered, porous,crystalline materials having a definite crystalline structure asdetermined by x-ray diffraction, within which there are a large numberof smaller cavities which may be interconnected by a number of stillsmaller channels or pores. The dimensions of these channels or pores aresuch as to allow for adsorption of molecules with certain dimensionswhile rejecting those of large dimensions. The interstitial spaces orchannels formed by the crystalline network enable molecular sieves suchas crystalline silicates, crystalline aluminosilicates crystallinesilicoalumino phosphates, and crystalline aluminophosphates, to be usedas molecular sieves in separation processes and catalysts and catalystsupports in a wide variety of hydrocarbon conversion processes.

Zeolites are comprised of a lattice of silica and optionally aluminacombined with exchangeable cations such as alkali or alkaline earthmetal ions. Although the term "zeolites" includes materials containingsilica and optionally alumina, it is recognized that the silica andalumina portions may be replaced in whole or in part with other oxides.For example, germanium oxide, tin oxide, phosphorous oxide, and mixturesthereof can replace the silica portion. Boron oxide, iron oxide,titanium oxide, gallium oxide, indium oxide, and mixtures thereof canreplace the alumina portion. Accordingly, the terms "zeolite","zeolites" and "zeolite material", as used herein, shall mean not onlymaterials containing silicon and, optionally, aluminum atoms in thecrystalline lattice structure thereof, but also materials which containsuitable replacement atoms for such silicon and aluminum, such assilicoaluminophosphates (SAPO) and aluminophosphates (ALPO). The term"aluminosilicate zeolite", as used herein, shall mean zeolite materialsconsisting essentially of silicon and aluminum atoms in the crystallinelattice structure thereof.

Zeolites such as ZSM-5, that have been combined with a Group VIII metalhave been used in the past as catalysts for hydrocarbon conversion. Forexample, U.S. Pat. No. 3,856,872 discloses a zeolite preferablycontaining a binder such as aluminia that has been loaded with platinumby impregnation or ion exchange. A problem associated with zeolitecatalysts that have been loaded with metals by impregnation or ionexchange is that the metal may not be well dispersed. If the metal isnot well dispersed, selectivity, activity and/or activity maintenance ofthe zeolite catalyst can be adversely effected.

U.S. Pat. No. 4,312,790 discloses another method of loading platinum onan alumina bound zeolite. The method involves adding the noble metal tothe zeolite after crystallization of the zeolite, but beforecalcination. Catalysts prepared by this method have not beencommercially useful because, as reported in U.S. Pat. No. 4,683,214, theuse of the method has resulted in catalysts with poor platinumdispersion and large platinum crystallites.

Synthetic zeolites are normally prepared by the crystallization ofzeolites from a supersaturated synthesis mixture. The resultingcrystalline product is then dried and calcined to produce a zeolitepowder. Although the zeolite powder has good adsorptive properties, itspractical applications are severely limited because it is difficult tooperate fixed beds with zeolite powder. Therefore, prior to using thepowder in commercial processes, the zeolite crystals are usually bound.

The zeolite powder is typically bound by forming a zeolite aggregatesuch as a pill, sphere, or extrudate. The extrudate is usually formed byextruding the zeolite in the presence of a non-zeolitic binder anddrying and calcining the resulting extrudate. The binder materials usedare resistant to the temperatures and other conditions, e.g., mechanicalattrition, which occur in various hydrocarbon conversion processes.Examples of binder materials include amorphous materials such alumina,silica, titania, and various types of clays. It is generally necessarythat the zeolite be resistant to mechanical attrition, that is, theformation of fines which are small particles, e.g., particles having asize of less than 20 microns.

Although such bound zeolite aggregates have much better mechanicalstrength than the zeolite powder, when such a bound zeolite is used in acatalytic conversion process, the performance of the zeolite catalyst,e.g., activity, selectivity, activity maintenance, or combinationsthereof, can be reduced because of the binder. For instance, since thebinder is typically present in an amount of up to about 50 wt. % ofzeolite, the binder dilutes the adsorption properties of the zeoliteaggregate. In addition, since the bound zeolite is prepared by extrudingor otherwise forming the zeolite with the binder and subsequently dryingand calcining the extrudate, the amorphous binder can penetrate thepores of the zeolite or otherwise block access to the pores of thezeolite, or slow the rate of mass transfer to the pores of the zeolitewhich can reduce the effectiveness of the zeolite when used in xyleneisomerization. Furthermore, when the bound zeolite is used in catalyticconversion processes, the binder may affect the chemical reactions thatare taking place within the zeolite and also may itself catalyzeundesirable reactions which can result in the formation of undesirableproducts.

In certain hydrocarbon conversion processes involving dehydrogenationand dehydrocyclization reactions, it is desirable that the zeolitecatalyst used in the process be effective for metal-catalyzed reactions,e.g., conversion of paraffins to aromatic products. In order for thecatalyst to be effective for metal catalyzed reactions, a catalyticallyactive metal is usually included in the catalyst. The catalyticallyactive metal should be uniformly dispersed. If the metal is notuniformly dispersed, the activity, selectivity, and/or activitymaintenance of the catalyst can be adversely effected.

Accordingly, it would be desirable to produce zeolite catalysts whichhave uniformly dispersed hydrogenation/dehydrogenation metals and do notcontain substantial amounts of non-zeolitic binder.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided a zeolitebound zeolite catalyst and a process for preparing the zeolite boundzeolite catalyst. The catalyst comprises first crystals of a firstzeolite, a binder comprising second crystals of a second zeolite, and ahydrogenation/dehydrogenation metal. The process is carried out byconverting the silica binder of a silica bound extrudate which alsocontains the first crystals of the first zeolite and thehydrogenation/dehydrogenation metal, into the second zeolite.

In another embodiment, the present invention provides a process for theconversion of hydrocarbon feeds using the zeolite bound zeolite catalystin a process or combination of processes which employs ahydrogenation/dehydrogenation metal such as a Group VIII metal. Examplesof such processes include hydrogenation, dehydrogenation,dehydrocyclization, isomerization, cracking, dewaxing, reforming,conversion of alkylaromatics, oxidation, synthesis gas conversion,hydroformylation, dimerization, polymerization, and alcohol conversion.

When used in processes such as naphtha reforming and xyleneisomerization, the zeolite bound zeolite catalyst exhibits highhydrogenation/dehydrogenation activity which results in the productionof desired products while at the same time exhibits reduced crackingactivity which is undesirable in these processes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 represents an electron micrograph of the catalyst prepared inExample 1.I.

FIG. 2 represents an electron micrograph of the catalyst prepared inExample 1.II.

DETAILED DESCRIPTION OF THE INVENTION

The zeolite bound zeolite catalyst comprises first crystals of a firstzeolite, a binder comprising second crystals of a second zeolite, and ahydrogenation/dehydrogenation metal. In preparing the zeolite boundzeolite catalyst, the hydrogenation/dehydrogenation metal is present inthe silica bound extrudate which contains the first zeolite prior toconverting the silica binder to the second zeolite. The resultingzeolite bound zeolite catalyst has enhancedhydrogenation/dehydrogenation metal dispersion. In addition, the use ofthe second crystals of the second zeolite as a binder results in acatalyst which provides a means for controlling undesirable reactionstaking place on or near the external surface of the first zeolitecrystals and can have improved mass transfer of hydrocarbon molecules toand from the pores of the first zeolite.

Unlike typical zeolite catalysts used in hydrocarbon conversionprocesses which are normally bound with silica or alumina or othercommonly used amorphous binders to enhance the mechanical strength ofthe zeolite, the zeolite catalyst of the present invention generallydoes not contain significant amounts of non-zeolitic binders.

Preferably, the zeolite bound zeolite catalyst contains less than 10percent by weight, based on the weight of the first and second zeolite,of non-zeolitic binder, more preferably contains less than 5 percent byweight, and, most preferably, the catalyst is substantially free ofnon-zealitic binder. Preferably, the second zeolite crystals bind thefirst zeolite crystals by adhering to the surface of the first zeolitecrystals thereby forming a matrix or bridge structure which also holdsthe first crystals particles together. More preferably, the secondzeolite particles bind the first zeolite by intergrowing so as to form acoating or partial coating on the larger first zeolite crystals and,most preferably, the second zeolite crystals bind the first zeolitecrystals by intergrowing to form an attrition resistant over-growth overthe first zeolite crystals.

Although the invention is not intended to be limited to any theory ofoperation, it is believed that in addition to enhanced metal dispersion,another advantage of the zeolite bound zeolite catalyst of the presentinvention is obtained by the second zeolite crystals controlling theaccessibility of the acid sites on the external surfaces of the firstzeolite to reactants. Since the acid sites existing on the externalsurface of a zeolite catalyst are not shape selective, these acid sitescan adversely affect reactants entering the pores of the zeolite andproducts exiting the pores of the zeolite. In line with this belief,since the acidity and structure type of the second zeolite can becarefully selected, the second zeolite does not significantly adverselyaffect the reactants exiting the pores of the first zeolite which canoccur with conventionally bound zeolite catalysts and may beneficiallyaffect the reactants exiting the pores of the first zeolite. Stillfurther, since the second zeolite is not amorphous but, instead, is amolecular sieve, hydrocarbons may have increased access to the pores ofthe first zeolite during hydrocarbon conversion processes. Regardless ofthe theories proposed, the zeolite bound zeolite catalyst, when used incatalytic processes, has one or more of the improved properties whichare disclosed herein.

The terms "acidity", "lower acidity" and "higher acidity" as applied tozeolite are known to persons skilled in the art. The acidic propertiesof zeolite are well known. However, with respect to the presentinvention, a distinction must be made between acid strength and acidsite density. Acid sites of a zeolite can be a Bronsted acid or a Lewisacid. The density of the acid sites and the number of acid sites areimportant in determining the acidity of the zeolite. Factors directlyinfluencing the acid strength are (i) the chemical composition of thezeolite framework, i.e., relative concentration and type of tetrahedralatoms, (ii) the concentration of the extra-framework cations and theresulting extra-framework species, (iii) the local structure of thezeolite, e.g., the pore size and the location, within the crystal orat/near the surface of the zeolite, and (iv) the pretreatment conditionsand presence of co-adsorbed molecules. The amount of acidity is relatedto the degree of isomorphous substitution provided, however, suchacidity is limited to the loss of acid sites for a pure SiO₂composition. As used herein, the terms "acidity", "lower acidity" and"higher acidity" refers to the concentration of acid sites irregardlessof the strength of such acid sites which can be measured by ammoniaabsorption.

First and second zeolites suitable for use in the zeolite bound zeolitecatalyst of the present invention include large pore size zeolites,intermediate pore size zeolites, and small pore size zeolites. Thesezeolites are described in "Atlas of Zeolite Structure Types", eds. W. H.Meier and D. H. Olson, Butterworth-Heineman, Third Edition, 1992, whichis hereby incorporated by reference. A large pore zeolite generally hasa pore size greater than about 7 Å and includes for example LTL, VFI,MAZ, MEI, FAU, EMT, OFF, BEA, and MOR structure type zeolites (IUPACCommission of Zeolite Nomenclature). Examples of large pore zeolites,include, for example, mazzite, mordenite, offretite, zeolite L, VPI-5,zeolite Y, zeolite X, omega, Beta, ZSM-3, ZSM-4, ZSM-18, and ZSM-20. Anintermediate pore size zeolite generally has a pore size from about 5 Å,to about 7 Å and includes for example, MFI, MFS, MEL, MTW, EUO, MTT,HEU, FER, and TON structure type zeolites (IUPAC Commission of ZeoliteNomenclature). Examples of intermediate pore size zeolites, includeZSM-5, ZSM-12, ZSM-22, ZSM-23, ZSM-34, ZSM-35, ZSM-38, ZSM-48, ZSM-50,silicalite, and silicalite 2. A small pore size zeolite generally has apore size from about 3 Å to about 5.0 Å and includes for example, CHA,ERI, KFI, LEV, and LTA structure type zeolites (IUPAC Commission ofZeolite Nomenclature). Examples of small pore zeolites include ZK-4,SAPO-24, SAPO-35, ZK-14, SAPO-42, ZK-21, ZK-22, ZK-5, ZK-20, zeolite A,erionite, chabazite, zeolite T, gemlinite, ALPO-17, and clinoptilolite.

Generally, the first and second zeolites of the zeolite bound zeolitecatalyst comprise compositions having the following molar relationship:

    X.sub.2 O.sub.3: :(n)YO.sub.2,

wherein X is a trivalent element, such as titanium, boron, aluminum,iron, and/or gallium, Y is a tetravalent element such as silicon, tin,and/or germanium, and n has a value of at least 1, said value beingdependent upon the particular type of zeolite and the trivalent elementpresent in the zeolite.

When either zeolite has an intermediate pore size, the zeolite usuallycomprises a composition having the following molar relationship:

    X.sub.2 O.sub.3: :(n)YO.sub.2,

wherein X is a trivalent element, such as aluminum, boron, titanium,and/or gallium, Y is a tetravalent element such as silicon, tin, and/orgermanium; and n has a value greater than 10, said value being dependentupon the particular type of zeolite and the trivalent element present inthe zeolite. When the first or second zeolite has a MFI structure, n ispreferably greater than 10.

As known to persons skilled in the art, the acidity of a zeolite can bereduced using many techniques such as by dealumination and steaming. Inaddition, the acidity of a zeolite is dependent upon the form of thezeolite with the hydrogen form having the highest acidity and otherforms of the zeolite such as the sodium form having less acidity thanthe acid form. Accordingly, the mole ratios of silica to alumina andsilica to gallia disclosed herein shall include not only zeolites havingthe disclosed mole ratios, but shall also include zeolites not havingthe disclosed mole ratios but having equivalent catalytic activity.

When the first zeolite is a gallium silicate intermediate pore sizezeolite, the zeolite usually comprises a composition having thefollowing molar relationship:

    Ga.sub.2 O.sub.3 :ySiO.sub.2

wherein y is between about 10 and about 1000. The zeolite framework maycontain only gallium and silicon atoms or may also contain a combinationof gallium, aluminum, and silicon. When the first zeolite is a MFIstructure type gallium silicate zeolite, the second zeolite willpreferably be an intermediate pore size zeolite having a silica togallia mole ratio greater than 100. The second zeolite can also havehigher silica to gallia mole ratios, e.g., greater than 200, 500, 1000,etc.

When the first zeolite in the zeolite bound zeolite catalyst is analuminosilicate zeolite, the silica to alumina mole ratio will usuallydepend upon the structure type of the first zeolite and the particularhydrocarbon process in which the catalyst is utilized and is thereforenot limited to any particular ratio. Generally, however, and dependingon the structure type of the zeolite, the first zeolite will have asilica to alumina mole ratio of at least 2:1 and in some instances from4:1 to about 7:1. For a number of zeolites, the silica to alumina moleratio will be in the range of from about 10:1 to about 1,000:1. Inapplications such as when the catalyst is utilized in acid catalyzedreactions, e.g., the isomerization of a feedstream containing xylenesand ethylbenzene, the first zeolite will be acidic and will preferably,especially when an intermediate pore size zeolite, have higher silica toalumina mole ratios, e.g., 70:1 to about 700:1. If the catalyst is usedin hydrocarbon conversion processes where acid catalyzed reactions arenot desired, e.g., zeolite L reforming, the first zeolite willpreferably exhibit reduced acid activity and, more preferably willexhibit little or no acid activity. For these types of processes, theacid activity can be reduced by using high silica to alumina moleratios, by ion exchange or by other techniques known to persons skilledin the art.

The structure type of the first zeolite will depend on the particularhydrocarbon process in which the zeolite catalyst system is utilized.For instance, if the catalyst is used for the reforming of naphtha toaromatics, the zeolite type will preferably be LTL (example Zeolite L).If the catalyst is be used for xylene isomerization, the first zeolitewill preferably be an intermediate pore size zeolite, such as a MFIstructure type (example ZSM-5). If the catalyst is used for crackingparaffins, the preferred pore size and structure type will depend on thesize of the molecules to be cracked and the desired product. Theselection of the structure type for hydrocarbon conversion processes isknown to persons skilled in the art.

When the first zeolite is a LTL structure type, the zeolite ispreferably an aluminosilicate zeolite having a composition (expressed interms of molar ratios of the constituent oxides in anhydrous form) of:

    (0.9-1.3)M.sub.2/n O:Al.sub.2 O.sub.3 :xSiO.sub.2

wherein M is a cation of valence n, x is from 4 to 7.5, preferably from5 to 7.5.

When the zeolite bound zeolite catalyst is used for the isomerization ofa feedstream containing alkylaromatic hydrocarbons, the first zeolite ispreferably an aluminosilicate zeolite or a gallium silicate zeolite andthe zeolite will usually having a silica to alumina mole ratio from 70:1to 700:1 or a silica to gallia mole ratio from 24 to 500.

The term "average particle size" as used herein, means the arithmeticaverage of the diameter distribution of the crystals on a volume basis.

The average particle size of the crystals of the first zeolite ispreferably from about 0.1 to about 15 microns. In some applications, theaverage particle size will preferably be at least about 1 to about 6microns. In other applications such as the cracking of hydrocarbons, thepreferred average particle size is smaller, e.g., from about 0.1 toabout 3.0 microns.

The structure type of the second zeolite can be the same or can bedifferent from the first zeolite. The structure type of the secondzeolite will depend on the intended use of the zeolite bound zeolitecatalyst. For instance, if the catalyst system is to be tailored to be abifunctional catalyst, the first zeolite and second zeolite can beselected and tailored to perform the desired reactions.

When the second zeolite is aluminosilicate zeolite, the silica toalumina mole ratio of the second zeolite, will usually depend upon thestructure type of the second zeolite and particular hydrocarbon processin which the catalyst is utilized and is therefore not limited to anyparticular ratio. Generally, however, and depending on the structuretype of the zeolite, the silica to alumina ratio will be at least 2:1 togreater than 1000. In certain applications, it is desirable that thesecond zeolite have reduced acidity or even substantially no acidity. Inthose applications when the zeolite is an intermediate pore sizezeolite, such as a ZSM-5, the second zeolite will usually have a silicato alumina mole ratio of 200:1 or greater, e.g., 300:1, 500:1, 1,000:1,etc. In certain applications, the second zeolite will be a Silicalitei.e., a MFI structure type substantially free of aluminia or Silicalite2, i.e., a MEL structure type substantially free of aluminia. The poresize of the second zeolite will preferably be a pore size that does notadversely restrict access of the desired molecules of the hydrocarbonfeedstream to the pores of the first zeolite. For instance, when thematerial of the feedstream which are to be converted by the firstzeolite have a size from 5 Å to 6.8 Å, the second zeolite willpreferably be a large pore zeolite or a medium pore zeolite. The secondzeolite is usually present in the catalyst system in an amount in therange of from about 10 to 60% by weight based on the weight of the firstzeolite by the amount of second zeolite present will usually depend onthe hydrocarbon process in which the catalyst is utilized. Morepreferably the amount of second zeolite present is from about 20 toabout 50% by weight.

The second zeolite crystals usually have a smaller size than the firstzeolite particles and preferably have an average particle size of lessthan 1 micron, for example, from about 0.1 to about 0.5 micron. Thesecond zeolite crystals, bind the first zeolite crystals and preferablyintergrow and form an over-growth which coats or partially coats thefirst zeolite. Preferably, the coating is resistant to attrition.

The zeolite bound zeolite catalyst will contain ahydrogenation/dehydrogenation metal. Reference to thehydrogenation/dehydrogenation metal or metals is intended to encompasssuch metal or metals in the elemental state (i.e. zero valent) or insome other catalytically active form such as an oxide, sulfide, halide,carboxylate and the like. Such metals are known to persons skilled inthe art and include, for example, one or more metals, and metals ofGroups IIIA, IVA, VA, VIA, VIIA, VIII, IB, IIB, IIIB, IVB, and VB of thePeriodic Table of the Elements. Examples of suitable metals includeGroup VIII metals (i.e., Pt. Pd, Ir, Rh, Os, Ru, Ni, Co and Fe), GroupIVA metals (i.e., Sn and Pb), Group VB metals (i.e., Sb and Bi), andGroup VIIB metals (i.e., Mn, Tc and Re). Noble metals (i.e., Pt, Pd, Ir,Rh, Os and Ru) are sometimes preferred.

The amount of metal present in the zeolite bound zeolite catalyst willbe an effective amount which will generally be from about 0.001 to about10 percent by weight and, preferably 0.05 to 3.0 percent by weight. Theamount will vary with the nature of the metal, less of the highly activemetals, particularly platinum, being required than of the less activemetals.

In preparing the zeolite bound zeolite catalyst containing thehydrogenation/dehydrogenation metal, the metal will be present in asilica bound aggregate containing the first zeolite prior to convertingthe silica binder to the second zeolite of the zeolite bound zeolitecatalyst. The addition of the metal to the silica bound aggregate can beaccomplished at any stage prior to converting the silica binder to thesecond zeolite such as before, during, or after the formation of thesilica bound aggregate.

For example, the zeolite bound zeolite catalyst is preferably made usingthe following steps:

1. Prepare the first zeolite using known procedures.

2. Form an extrudate mass containing silica and the first zeolite.

3. Extrudate the mass to form a silica bound aggregate.

4. Calcine the silica bound aggregate.

5. Age the silica bound aggregate in an appropriate aqueous solution.

6. Convert the silica binder of the silica bound aggregate to the secondzeolite by aging.

The addition of the metal to the silica bound aggregate can take placeat any time prior to step 6, e.g., during steps 1-5. For example, themetal can be incorporated with the first zeolite prior to thecommencement of step 2 by co-crystallization of the metal and the firstzeolite or by loading metal on first zeolite by techniques such as ionexchange or impregnation. The metal can also be added during theformation of the extrudate mass, after formation of the silica boundaggregate, prior to calcination, after calcination, or during the agingof the silica bound aggregate. In a preferred embodiment, the metal isadded during step 2 by including the metal in the extrudable mass. Afterconverting the silica binder to the second zeolite, the metal can bepresent on the surface of either or both zeolites and may also bepresent in the intracrystalline matrix of either or both zeolites.

Catalysts produced by the method of the invention offer at least one ofthe following advantages: Improved metal dispersion, reduced crackingactivity while maintaining high hydrogenation/dehydrogenation activity,or combinations thereof.

The zeolite bound zeolite catalyst containing thehydrogenation/dehydrogenation metal is preferably prepared by a threestep procedure. The first step involves the synthesis of theintermediate pore size first zeolite. Process for preparing the firstzeolite are known to persons skilled in the art. For example, withrespect to the preparation of an aluminosilicate zeolite or a galliumsilicate zeolite having a MFI structure type, one process comprisespreparing a solution containing tetrapropyl ammonium hydroxide orbromide, alkali metal oxide, an oxide of aluminum or an oxide ofgallium, an oxide of silicon and water, heating the reaction mixture toa temperature of 80° C. to 200° for a period of from about four hours toeight days. The resulting gel forms solid crystal particles which areseparated from the reaction medium, washed with water and dried. Theresulting product can be calcined in air at temperatures of 400° C.-550°C. for a period of 10-40 hours to remove tetrapropylammonium TPA)cations.

In the second step, a silica-bound zeolite is prepared by mixing amixture comprising the first zeolite crystals, a silica gel or sol,water, and the hydrogenation/dehydrogenation metal or a compoundcontaining the metal, and optionally an extrusion aid, until ahomogeneous composition in the form of an extrudable paste develops. Thesilica used in preparing the silica bound zeolite aggregate ispreferably a silica sol and can contain various amounts of trivalentelements, e.g., aluminum or gallium. The amount of silica used is suchthat the content of the zeolite in the dried extrudate at this stagewill range from about 40 to 90% by weight, more preferably from about 50to 80% by weight, with the balance being primarily silica, e.g. about 20to 50% by weight silica.

The resulting paste is then molded, e.g., extruded, and cut into smallstrands, e.g., approximately 2 mm diameter extrudates, which are driedat 100° C. to 150° C. for a period of 4-12 hours and then are calcinedin air at a temperature of from about 400° C. to 550° C. for a period offrom about 1 to 10 hours.

Optionally, the silica-bound aggregate can be made into very smallparticles which have application in fluid bed processes such ascatalytic cracking. This preferably involves mixing the zeolite with asilica and metal containing matrix solution so that an aqueous solutionof zeolite and silica binder is formed which can be sprayed dried toresult in small fluidizable silica-bound aggregate particles. Proceduresfor preparing such aggregate particles are known to persons skilled inthe art. An example of such a procedure is described by Scherzer(Octane-Enhancing Zeolitic FCC Catalysts, Julius Scherzer, MarcelDekker, Inc. New York, 1990). The fluidizable silica-bound aggregateparticles, like the silica bound extrudates described above, would thenundergo the final step described below to convert the silica binder to asecond zeolite.

The final step in the three step catalyst preparation process is theconversion of the silica present in the silica-bound zeolite to a secondzeolite which binds the first zeolite crystals together.

To prepare the second zeolite, the silica-bound aggregate is first agedin an appropriate aqueous solution at elevated temperature. Next, thecontents of the solution and the temperature at which the aggregate isaged are selected to convert the amorphous silica binder into thedesired second zeolite. The newly-formed second zeolite is produced ascrystals. The crystals may grow on and/or adhere to the first zeolitecrystals, and may also be produced in the form of new intergrowncrystals, which are generally much smaller than the first crystals,e.g., of sub-micron size. These newly formed crystals may grow togetherand interconnect.

The nature of the zeolite formed in the second synthesis conversion ofthe silica to zeolite may vary as a function of the composition of thesecondary synthesis solution and synthesis aging conditions. Thesecondary synthesis solution is preferably an aqueous ionic solutioncontaining a source of hydroxy ions sufficient to covert the silica tothe desired zeolite. It is important, however, that the aging solutionbe of a composition which will not cause the silica present in the boundzeolite extrudate to dissolve out of the extrudate.

In a preferred embodiment of the invention, the aqueous ionic solutionin which the silica bound aggregate is aged contains a source of hydroxyions (Preferably NaOH). When manufacturing an MFI structure typezeolite, the initial molar ratio of OH to SIO₂ is preferably at a levelof up to about 1.2, more preferably from about 0.05 to 1.2, and mostpreferably from about 0.07 to 0.15. This treatment causes the silicabinder to be converted substantially to a MFI structure type zeolite,but of lower acidity as reflected by having a significantly highersilica to alumina ratio. The solution also contains a template (e.g.,source of tetraalkyl ammonium ions for MFI structure type zeolite) andmay optionally include a source of alumina and a source of Na⁺ ions. Thesilica to alumina ratio of the converted binder is thus controlled bycontrolling the composition of the aqueous solution.

It important that the aging solution have a pH which is not tooalkaline. This may be achieved, when producing a MFI structure typebound zeolite, by using a solution having an initial molar ratio ofOH:SiO₂ of 0.05 to 1.2. Generally, ratios of 0.07 to 0.15 are preferred.Aging of the zeolite extrudate in the aging solution is preferablyconducted at elevated temperatures, generally in the range of from about95 to 200° C., more preferably in the range of about 130 to 170° C.,most preferably in the range of about 145 to 155° C. Aging time mayrange from about 20 to 140 hours, more preferably from about 60 to 140hours, most preferably from about 70 to 80 hours. After aging, thezeolite bound zeolite is separated from solution, washed, dried andcalcined.

The first and second zeoltes of the zeoidte catalyst of the presentinvention may be further ion exchanged as is known in the art either toreplace at least in part the original alkali metal present in thezeolite with a different cation, e.g. a Group 1B to VIII Periodic Tableof Elements, or to provide a more acidic form of the zeolites byexchange of alkali metal with intermediate ammonium, followed bycalcination of the ammonium form to provide the acidic hydrogen form.The acidic form may be readily prepared by ion exchange using a suitableacidic reagent such as ammonium nitrate. The zeolite catalyst may thenbe calcined at a temperature of 400-550° C. for a period of 10-45 hoursto remove ammonia and form the acidic hydrogen form. Ion exchange ispreferably conducted after formation of the zeolite catalyst.

The zeolite bound zeolite catalysts of the present invention can be usedin processing hydrocarbon feedstocks. Hydrocarbon feed-stocks containcarbon compounds and can be from many different sources, such as virginpetroleum fractions, recycle petroleum fractions, tar sand oil, and, ingeneral, can be any carbon containing fluid susceptible to zeoliticcatalytic reactions. Depending on the type of processing the hydrocarbonfeed is to undergo, the feed can contain metal or can be free of metals.Also, the feed can also have high or low nitrogen or sulfur impurities.

The conversion of hydrocarbon feeds can take place in any convenientmode, for example, in fluidized bed, moving bed, or fixed bed reactorsdepending on the types of process desired.

The zeolite bound zeolite catalyst can be used as a catalyst for avariety of organic, e.g., hydrocarbon compound conversion processesincluding hydrogenation, dehydrogenation, dehydrocycization,isomerization, hydrocracking, dewaxing, reforming, conversion of alkylaromatics, oxidation, reforming, synthesis gas conversion,hydroformylation, dimerization, polymerization, alcohol conversion, etc.

Catalytic conversion conditions for hydrogenation of feedstocks such asalkenes, dienes, polyenes, alkynes, cyclenes, aromatics, oxygenates,etc. include a temperature of between about 0° F. and about 1000° F.,preferably between about 80° F. and 900° F., a pressure of between about10 psia and about 1000 psia, preferably between about 20 psia and 200psia, a hydrogen/feed mole ratio of between about 0.1 and 20, preferablybetween about 4 and 12 and a LHSV of between about 0.1 and 20,preferably between about 0.5 and 4.

Dehydrogenation conditions, for processes such as conversion ofparaffins to the corresponding olefins, or ethyl benzene to styrene,optionally in the presence of steam or inert gases such as nitrogen,include temperatures of from about 400° F. to 1800° F., preferably fromabout 650° F. to 1000° F.; feedstock partial pressures of from about10,000-1500 psia, preferably from about 2 psia to 20 psia and a LHSV offrom about 0.1 to 100, preferably between about 0.5 and 4.

Dehydrocyclization conditions, for example for conversion of paraffinsto aromatics (e.g., octane to ethylbenzene or xylene), includetemperatures of from about 400° F. to 1800° F., preferably from about600° F. to 1100° F.; feedstock partial pressures of from about 1 psia to1500 psia, preferably from about 2 psia to 20 psia) and a LHSV of fromabout 0.1 to 100, preferably between about 0.5 and 4.

Isomerization of normal paraffins, with or without hydrogen, isconducted at a temperature of between about 212° F. and 50° F.,preferably between about 400° F. and 900° F., a LHSV of between about0.01 and 20, preferably between about 0.25 and 5 and a hydrogen tohydrocarbon mole ratio of between 0 and 5:1.

Catalytic conversion conditions for cracking, with or without hydrogen,include a temperature of between about 1200° F. and about 100° F., apressure of between about 25 psia and about 2500 psia, a hydrogen/feedmole ratio of between about 0 and about 80 and a LHSV of between about0.1 and about 10.

The catalysts of the present invention are also useful in dewaxingoperations. Likewise, the invention can be used in reforming catalystsor as part of a reforming catalyst. Dewaxing and reforming can becarried out in the presence or absence of hydrogen under conditionswhich include a temperature of from about 500° F. to 1100° F.,preferably from about 800° F. to 950° F.; a pressure of from 1.5 psia to1470 psia and a WHSV of from about 0.01 to about 100, preferably fromabout 0.1 to 10.

Thus, exemplary hydrocarbon conversion processes which find particularapplication include the following:

(A) The catalytic cracking of a naphtha feed to produce light olefins.Exemplary reaction conditions include from about 500° C. to about 750°C., pressures of subatmospheric or atmospheric, generally ranging up toabout 10 atmospheres (gauge) and residence time (volume of the catalystfeed rate) from about 10 milliseconds to about 10 seconds.

(B) The catalytic cracking of high molecular weight hydrocarbons tolower molecular weight hydrocarbons. Exemplary reaction conditions forcatalytic cracking include temperatures of from about 400° C. to about700° C., pressures of from about 0.1 atmosphere (bar) to about 30atmospheres, and weight hourly space velocities of from about 0.1 toabout 100 hr⁻¹.

(C) The isomerization of aromatic (e.g., xylene) feedstock components.Exemplary reaction conditions for such include a temperature of fromabout 230° C. to about 510° C., a pressure of from about 0.5 atmospheresto about 50 atmospheres, a weight hourly space velocity of from about0.1 to about 200 and a hydrogen/hydrocarbon mole ratio of from about 0to about 100.

(D) The hydrocracking of heavy petroleum feedstocks, cyclic stocks, andother hydrocrack charge stocks. The zeolite catalyst system will containan effective amount of at least one hydrogenation component of the typeemployed in hydrocracking catalysts.

(E) The conversion of light paraffins to olefins and/or aromatics.Exemplary reaction conditions include temperatures from about 425° C. toabout 760° C. and pressures from about 10 to about 2000 psig.

(F) The conversion of light olefins to gasoline, distillate and luberange hydrocarbons. Exemplary reaction conditions include temperaturesof from about 175° C. to about 375° C. and a pressure of from about 100to about 2000 psig.

(G) Two-stage hydrocracking for upgrading hydrocarbon streams havinginitial boiling points above about 200° C. to premium distillate andgasoline boiling range products or as feed to further fuels or chemicalsprocessing steps. The first stage would be the zeolite catalystcomprising one or more catalytically active metals, e.g., a Group VIIImetal, and the effluent from the first stage would be reacted in asecond stage using a second zeolite, e.g., zeolite Beta, comprising oneor more catalytically active substances, e.g., a Group VIII metal, asthe catalyst. Exemplary reaction conditions include temperatures fromabout 315° C. to about 455° C., a pressure from about 400 to about 2500psig, hydrogen circulation of from about 1000 to about 10,000 SCF/bbland a liquid hourly space velocity (LHSV) of from about 0.1 to 10;

(H) A combination hydrocracking/dewaxing process in the presence of thezeolite bound zeolite catalyst comprising a hydrogenation component anda zeolite such as zeolite Beta. Exemplary reaction conditions includetemperatures from about 350° C. to about 400° C., pressures from about1400 to about 1500 psig, LHSVs from about 0.4 to about 0.6 and ahydrogen circulation from about 3000 to about 5000 SCF/bbl.

(I) The reaction of alcohols with olefins to provide mixed ethers, e.g.,the reaction of methanol with isobutene and/or isopentene to providemethyl-t-butyl ether (MTBE) and/or t-amyl methyl ether (TAME). Exemplaryconversion conditions include temperatures from about 20° C. to about200° C., pressures from 2 to about 200 atm, WHSV (gram-olefin per hourgram-zeolite) from about 0.1 hr⁻¹ to about 200 hr⁻¹ and an alcohol toolefin molar feed ratio from about 0.1/1 to about 5/1.

(J) The conversion of naphtha (e.g., C₆ -C₁₀) and similar mixtures tohighly aromatic mixtures. Thus, normal and slightly branched chainedhydrocarbons, preferably having a boiling range above about 40° C., andless than about 200° C., can be converted to products having asubstantial higher octane aromatics content by contacting thehydrocarbon feed with the zeolite at a temperature in the range of fromabout 400° C. to 600° C., preferably 480° C. to 550° C. at pressuresranging from atmospheric to 40 bar, and liquid hourly space velocities(LHSV) ranging from 0.1 to 15.

(K) The conversion of oxygenates, e.g., alcohols, such as methanol, orethers, such as dimethylether, or mixtures thereof to hydrocarbonsincluding olefins and aromatics with reaction conditions including atemperature of from about 275° C. to about 600° C., a pressure of fromabout 0.5 atmosphere to about 50 atmospheres and a liquid hourly spacevelocity of from about 0.1 to about 100;

(L) The oligomerization of straight and branched chain olefins havingfrom about 2 to about 5 carbon atoms. The oligomers which are theproducts of the process are medium to heavy olefins which are useful forboth fuels, i.e., gasoline or a gasoline blending stock, and chemicals.The oligomerization process is generally carried out by contacting theolefin feedstock in a gaseous state phase with a zeolite bound zeoliteat a temperature in the range of from about 250° C. to about 800° C., aLHSV of from about 0.2 to about 50 and a hydrocarbon partial pressure offrom about 0.1 to about 50 atmospheres. Temperatures below about 250° C.may be used to oligomerize the feedstock when the feedstock is in theliquid phase when contacting the zeolite bound zeolite catalyst. Thus,when the olefin feedstock contacts the catalyst in the liquid phase,temperatures of from about 10° C. to about 250° C. may be used.

(M) The conversion of C₂ unsaturated hydrocarbons (ethylene and/oracetylene) to aliphatic C₆₋₁₂ aldehydes and converting said aldehydes tothe corresponding C₆₋₁₂ alcohols, acids, or esters.

(N) The conversion of alkylaromatic hydrocarbons such as thedealkylation of ethylbenzene to benzene.

(O) The saturation of olefins having from 2 to 20 carbon atoms.

(P) The isomerization of ethylbenzene to xylenes. Exemplary conversionconditions include a temperature from 600°-800° F., a pressure of from50 to about 500 psig and a LHSV of from about 1 to about 10.

In general, the, catalytic conversion conditions over the zeolitecatalyst of the invention independently and in combination include atemperature of from about 100° C. to about 760° C., a pressure of fromabout 0.1 atmosphere (bar) to about 200 atmospheres (bar), a weighthourly space velocity of from about 0.08 hr⁻¹ to about 2,000 hr⁻¹.

Although many hydrocarbon conversion processes prefer that the secondzeolite crystals have lower acidity, some processes prefer that thesecond zeolite crystals have higher acidity.

Processes that find particular application using the zeolite boundzeolite catalyst are those where two or more reactions are taking placewithin the zeolite catalyst system. The zeolite bound zeolite catalystwould comprise two different zeolites that are each separately tailoredto promote or inhibit different reactions. A process using such acatalyst benefits not only from greater apparent catalyst activity,greater zeolite accessibility, and reduced non-selective surface aciditypossible with zeolite bound zeolites, but from a tailored catalystsystem.

The zeolite bound zeolite catalyst finds particular application forisomerizing one or more xylene isomers in a C₈ aromatic feed containingethylbenze to obtain ortho-, meta-, and para-xylene in a ratioapproaching the equilibrium value while substantially convertingethylbenzene. In particular, xylene isomerization is used in conjunctionwith a separation process to manufacture para-xylene. For example, aportion of the para-xylene in a mixed C₈ aromatics stream may berecovered using processes known in the art, e.g., crystallization,adsorption, etc. The resulting stream is then reacted under xyleneisomerization conditions to restore ortho-, meta-, and paraxylenes to anear equilibrium ratio. At the same time, it is also desirable thatethylbenzene in the feed be converted with very little net loss ofxylenes. The acidity of the first zeolite and second zeolite of thezeolite bound zeolite catalyst can be selected to balance xyleneisomerization and ethylbenzene dealkylation while minimizing undesirableside reactions, e.g., ethylation of xylenes andethylbenzene/ethylbenzene or ethylbenzene/xylene transalkylation. Theisomerization process is carried out by contacting a C₈ aromatic streamcontaining one or more xylene isomers or ethylbenzene or mixturesthereof, under isomerization conditions with the zeolite bound zeolitecatalyst. The catalyst of the present invention is useful in saturatingethylene formed during ethylbenzene dealkylation and offers the benefitof reduced aromatics saturation and subsequent cracking of naphthenes.

Suitable isomerization conditions include a temperature in the range of250° C.-600° C., preferably 300° C.-550° C., a pressure in the range0.5-50 atm abs, preferably 10-25 atm abs, and a weight hourly spacevelocity (WHSV) of 0.1 to 100, preferably 0.5 to 50. Optionally,isomerization in the vapor phase is conducted in the presence of 0.1 to30.0 moles of hydrogen per mole of alkylbenzene. If hydrogen is used,the catalyst should comprise 0.1 to 2.0 wt. % of ahydrogenation/dehydrogenation component selected from Group VIIIA of thePeriodic Table, especially platinum, palladium, or nickel. By Group VIIImetal component is meant that the metals or their compounds such asoxides and sulfides.

The zeolite bound zeolite catalysts find particular application inreactions involving aromatization and/or dehydrogenation. They areparticularly useful in a process for the dehydrocyclization and/orisomerization of acyclic hydrocarbons in which the hydrocarbons arecontacted at a temperature of from 370° C. to 600° C., preferably from430° C. to 550° C. with the zeolite bound zeolite catalyst, preferablyzeolite L bound by zeolite L, preferably having at least 90% of theexchangeable cations as alkali metal ions and incorporating at least oneGroup VIII metal having dehydrogenating activity, so as to convert atleast part of the acyclic hydrocarbons into aromatic hydrocarbons.

The aliphatic hydrocarbons may be straight or branched chain acyclichydrocarbons, and particularly paraffins such as hexane, althoughmixtures of hydrocarbons may also be used such as paraffin fractionscontaining a range of alkanes possibly with minor amounts of otherhydrocarbons. Cycloaliphatic hydrocarbon such as methylcyclopentane mayalso be used. In a preferred embodiment, the feed to a process forpreparing aromatic hydrocarbons and particularly benzene compriseshexanes. The temperature of the catalytic reaction may be from 370° C.to 600° C., preferably 430° C. to 550° C. and preferably pressures inexcess of atmospheric are used, for example up to 2000 KPa, morepreferably 500 to 1000 KPa. Hydrogen is usually employed in theformation of aromatic hydrocarbons preferably with a hydrogen to feedratio of less than 10. The following examples illustrate the invention:

EXAMPLE 1

Preparation of Zeolite Bound MFI Type Gallium Silicate Catalyst

I. Catalyst A--Platinum Loaded During Synthesis

MFI structure gallium silicate crystals were prepared as follows:

    ______________________________________                                        Components Use       Quantity                                                 for Preparation      (Grams)                                                  ______________________________________                                        Solution A                                                                    NaOH pellets (98.6%) 18.82                                                    Ga.sub.2 O.sub.3 (99.999%)                                                                         12.06                                                    Water                50.08                                                    Rinse Water          189.80                                                   Solution B                                                                    Colloidal Silica (Ludox HS-40)                                                                     773.06                                                   Solution C                                                                    Tetrapropylammonium bromide                                                                        123.73                                                   Water                425.01                                                   Rinse Water          124.97                                                   Solution D                                                                    Aqueous Suspension of Colloidal                                                                    2.39                                                     Silicalite with 0.0794 wt. % Seeds                                            Rinse Water          100.00                                                   ______________________________________                                    

The ingredients of Solution A were dissolved by boiling until a clearsolution was obtained. Solution A was then cooled to ambient temperatureand water loss from boiling was corrected.

Solution B was poured into a 2 liter glass beaker. Solution C was pouredinto the contents of the beaker and mixed. Solution D was then pouredinto the contents of the beaker and the beaker content was mixed. Thecontents of the beaker were poured into a 2 liter stainless steelautoclave. Rinse Water was used to rinse the beaker and added to theautoclave. Solution A were added to the autoclave. The contents of theautoclave were mixed about 20 minutes. A smooth pourable gel wasobtained. The gel had the following composition expressed in moles ofpure oxide:

    0.45 Na.sub.2 O/0.90 TPA Br/0.125 Ga.sub.2 O.sub.3 /10SiO.sub.2 /147 H.sub.2 O

The gel contained 1.0 wt ppm of colloidal silicalite seeds.

The autoclave was placed in an oven and heated to 150° C. in 2 hours andmaintained at 150° C. at this temperature for 48 hours.

The product was removed from the autoclave and divided into 3 portions.Each portion was washed 7 times with about 600 grams of water. Theproduct was dried over night at 120° C. The amount of product recoveredwas 333.70 grams. The product was calcined in air at 475° C. for 48hours. The characteristics of the calcined product were the following:

XRD: Pure MFI

SEM: 4 micron size spherical crystals

Elemental: SiO₂ /Ga₂ O₃ =80

A portion of the calcined product was formed into silica bound 2 mmextrudates as follows:

    ______________________________________                                        Components Used      Quantity                                                 for Preparation      Grams                                                    ______________________________________                                        Silica Sol (Nyacol 2034 DI)                                                                        128.59                                                   Silica gel (aerosil 300)                                                                           12.26                                                    H.sub.2 PtCl.sub.6.6H.sub.2 O                                                                      2.47                                                     Water                35.01                                                    Rinse Water          3.00                                                     Gallium silicate MFI Crystals                                                                      130.00                                                   Extrusion Aid        0.87                                                     (hydroxypropyl methyl cellulose)                                              ______________________________________                                    

The components were mixed in a food mixer in the order shown. Afteradding the extrusion aid and mixing for about 7 minutes, a thick andsmooth paste was obtained. The paste was extruded into 2 mm extrudatesand dried at ambient temperature for 3 hours. The extrudates were brokeninto smaller 5 mm pieces and dried in an oven at 120° C. for 16 hours.The dried extrudates were calcined at 490° C. for 8 hours in air.

Composition of calcined silica bound extrudate:

Silica binder: 30.1 wt. %

MFI: 69.4 wt. %

Platinum 0.5 wt. %

The silica bound extrudates were converted into zeolite bound zeolite asfollows:

    ______________________________________                                        Components Used     Quantity                                                  for Preparation     (Grams)                                                   ______________________________________                                        Solution A                                                                    NaOH pellets (98.6%)                                                                              1.36                                                      Water               29.08                                                     Rinse Water         11.78                                                     Solution B                                                                    Tetrapropylammonium bromide                                                                       9.28                                                      Water               30.35                                                     Rinse Water         22.16                                                     ______________________________________                                    

Solutions A and B were poured into a 1 liter autoclave and mixed.Finally, 70.0 grams of the silica bound extrudates were added to theautoclave. The molar composition of the synthesis mixture was:

    0.48Na.sub.2 O/1.00TPABr/10S.sub.i O.sub.2 /149H.sub.2 O

The autoclave was placed into an oven. The oven was heated from roomtemperature to 150° C. in 2 hours and maintained at this temperature for80 hours. The resulting product was washed at 60° C. 4 times with 1700ml of water. The conductivity of the last wash water was 49 μS/cm. Theextrudates were dried at 120° C. and calcined in air at 490° C. for 16hours.

The product was analyzed by XRD and SEM with the following results:

XRD: Excellent crystallinity

SEM: 4 micron size crystals coated with smaller size crystals. Novisible amorphous silica.

Elemental:

Core crystals: S_(i) O₂ /Ga₂ O₃ =80

Binder crystals=silicalite

Core crystals=70 wt. %

Platinum=0.5 wt. %

Platinum distribution and platinum particle size were determined byqualitatively examining a sample of the product by transmission electronmicroscopy (TEM) using a Philips CM12 TEM. FIG. 1 represents an electronmicrograph of the Catalyst A. The images of the micrograph indicate thatplatinum was distributed well. The major proportion of the platinum hada particle size of 5-10 nm.

II. Catalyst B--Platinum Loaded by Pore Filling

A portion of the calcined MFI structure type gallium silicate used toprepare Catalyst A was formed into silica bound 2 mm extrudates asfollows:

    ______________________________________                                        Components Used      Quantity                                                 for Preparation      (Grams)                                                  ______________________________________                                        Gallium-silicate MFI crystals                                                                      130.05                                                   Water                37.70                                                    SlO.sub.2 gel (aerosil 300)                                                                        45.26                                                    Silica Sol (NALCOAG 1034A)                                                                         128.57                                                   Extrusion aid        0.89                                                     (hydroxypropyl methyl cellulose)                                              ______________________________________                                    

The above components were mixed in a food mixer in the order shown.After adding the extrusion aid and mixing for about 14 minutes, a thickand smooth paste was obtained. The paste was extruded into 2 mmextrudates. The extrudates were dried at 150° C. for 7 hours and thencalcined in air at 510° C. for 8 hours.

Composition of calcined silica-bound extrudates:

MFI: 70.0 wt. %

S_(i) O₂ binder: 30.0 wt. %

The silica bound extrudates were converted into zeolite bound zeolite asfollows:

    ______________________________________                                        Components Used     Quantity                                                  for Preparation     (Grams)                                                   ______________________________________                                        Solution A                                                                    NaOH pellets (98.6%)                                                                              2.44                                                      Water               51.91                                                     Rinse Water         21.08                                                     Solution B                                                                    Tetrapropylammonium bromide                                                                       16.56                                                     Water               54.20                                                     Rinse Water         39.54                                                     ______________________________________                                    

Solution A and B were poured into a 300 ml stainless steel autoclave andwere mixed. Finally, 125.00 grams of the silica-bound MFI extrudateswere added to the autoclave. The molar composition of the synthesismixture was:

    0.48Na.sub.2 O/0.99 TPA Br/SiO.sub.2 /148H.sub.2 O

In this mixture, the silica is present as the binder in the extrudate.

The autoclave was placed into an oven at room temperature, heated to150° C. within 2 hours, and maintained at 150° C. for 72 hours. Theresulting product was washed at 60° C. with 7 portions of 2000 ml ofwater. The conductivity of the last wash water was 25 μS/cm. The productwas dried at 150° C. and calcined in air at 500° C. for 16 hours.

The resulting product was characterized by x-ray diffraction (XRD) andscanning electron microscopy (SEND with the following results:

XRD: Excellent crystallinity

SEM: 4 micron MFI crystals coated with smaller size crystals. No visibleamorphous silica.

Elemental:

Core crystals: S_(i) O₂ /Ga₂ O₃ =80

Binder crystals=silicalite

Core crystals=70 wt. %

Binder crystals=30 wt. %

An amount of 0.31 wt. % of platinum (based on the weight of product) wasloaded into the catalyst. The process was carried out by firstexchanging the catalyst at 65° C. with a 1 normal NH₄ Cl solution. Theexchanged catalyst was washed with water, dried, and then calcined at530° C. for 8 hours. The loading of the platinum was done by thepore-filling method with an appropriate amount of Pt (NH₃)₄ Cl₂dissolved in water. After loading, the catalyst was dried and calcinedat 480° C. for 8 hours.

Platinum distribution and platinum particle size were determined byqualitatively examining a sample of the product by transmission electronmicroscopy (TEM) using a Philips C12 TEM. FIG. 2 represents an electronmicrograph of Catalyst B. The images of the micrograph indicate that theplatinum particle size was predominantly 10-30 nm and platinum was notas well distributed as Catalyst A.

EXAMPLE 2

I. Catalyst A--Combined Xylene Isomerization/Ethylbenzene DealkylationTests

A series of combined xylene isomerization/ethylbenzene dealkylationtests were conducted using Catalyst A by passing an xylenes rich feedthrough a fixed bed reactor. Catalyst A was pretreated in H₂ for two (2)hours at 850° F. and 250 psig. After the temperature had been lowered to700° F., the catalyst was presulfided to breakthrough with about 500 ppmH₂ S in H₂ at 250 psig. The subsequent on-oil tests were run at varyingconditions. The conditions and results are shown in Table I below:

                  TABLE I                                                         ______________________________________                                                   Run No.                                                                       1     2       3       4     5                                      ______________________________________                                        Temperature (°F.)                                                                   750     750     750   795   750                                  HC Partial Pressure                                                                        163     118     118   118   163                                  (inlet)                                                                       H.sub.2 Partial Pressure                                                                   81      118     118   118   81                                   (inlet)                                                                       WHSV (#/#/Hr)                                                                              10      3.7     10    20    10                                   H.sub.2 :Oil Ratio (Molar)                                                                 0.5     1.0     1.0   1.0   0.5                                  Hours On-Oil 155     431     481   621   748                                  Feed EB Wt.% 11.4    12.6    12.6  12.6  12.6                                 Feed Xylenes Wt. %                                                                         86.8    85.3    85.3  85.3  85.3                                 Feed PX Wt. %                                                                              2.7     1.1     1.1   1.1   1.1                                  % EB reacted 73.7    93.5    73.0  74.3  74.7                                 Ring Loss (% of feed                                                                       0.1     *-0.1   *-0.1 *-0.2 *-0.2                                aromatic rings)                                                               Xylenes Loss (% of feed                                                                    2.0     5.9     2.3   2.5   2.5                                  xylenes)                                                                      PX approach to                                                                             103     101     101   98    100                                  equilibrium (%)                                                               ______________________________________                                         *Negative values believed due to minor gas chromatography variations.    

The percent, % EB reacted was determined by the formula: % EBConv=100×(moles of EB in feed-moles of EB in product)/(moles of EB infeed); Aromatics ring loss % was determined by the formula: 100 ×(molesof aromatics in feed-moles of aromatics in product)/(moles of aromaticsin feed). Loss of xylenes was determined by the formula: 100×(moles ofxylenes in feed-moles of xylenes in product)/(moles of xylenes in feed)and PX approach to equilibrium was determined by the formula: (ProductPX/Xs-Feed PX/Xs)/(Equilibrium PX/Xs-Feed PX/Xs)X100.

II. Catalyst B--Combined Xylene Isomerization/Ethylbenzene DealkylationTests

A series of combined xylene isomerization/ethylbenzene dealkylationtests were conducted using Catalyst B by passing an artificial feedthrough a fixed bed reactor. Catalyst B was pretreated in H₂ andpresulfided using the same procedure described in Example II. Thesubsequent on-oil tests were run at varying conditions. The conditionsand results are shown in Table II below:

                  TABLE II                                                        ______________________________________                                                   Run No.                                                                       1     2       3       4     5                                      ______________________________________                                        Temperature (°F.)                                                                   736     750     710   786   736                                  HC Partial Pressure                                                                        163     118     118   118   118                                  H.sub.2 Partial Pressure                                                                   81      118     118   118   118                                  WHSV (#/#/Hr)                                                                              10      10      5     20    10                                   H.sub.2 :Oil Ratio (Molar)                                                                 0.5     1.0     1.0   1.0   1.0                                  Hours On-Oil 160     233     633   656   714                                  Feed EB Wt. %                                                                              12.3    12.6    12.6  12.6  12.6                                 Feed Xylenes Wt. %                                                                         85.3    85.3    85.3  85.3  85.3                                 Feed PX Wt. %                                                                              7.2     1.1     1.1   1.1   1.1                                  % EB reacted 72      78.3    75.8  74.0  69.4                                 Ring Loss (% of feed                                                                       0.1     1.3     1.2   0.6   1.0                                  aromatic rings)                                                               Xylenes Loss (% of feed                                                                    3.3     4.2     3.7   3.4   2.9                                  xylenes)                                                                      PX approach to                                                                             102     101     101   99    101                                  equilibrium (%)                                                               ______________________________________                                    

The data in the Tables shows that at comparable ethylbenzene conversion,ring loss and xylene loss for Catalyst A were significantly lower thanfor Catalyst B. Both Catalyst A and Catalyst were effective inisomerizing xylenes and converting ethylbenzene.

EXAMPLE 3

Preparation of Zeolite KL Bound by Zeolite KL

I. Catalyst C--Platinum Loaded During Synthesis.

LTL structure aluminosilicate crystals (zeolite KL) were prepared asfollows:

    ______________________________________                                        Components Use      Quantity                                                  for Preparation     (Grams)                                                   ______________________________________                                        Solution A                                                                    KOH pellets (87.0%) 176.3                                                     Al(OH).sub.3        81.7                                                      Water               837.2                                                     Solution B                                                                    Colloidal Silica (Ludox HS-40)                                                                    786.9                                                     Rinse Water         104.8                                                     ______________________________________                                    

The ingredients of Solution A were dissolved by boiling until a clearsolution was obtained. Solution A was then cooled to ambient temperatureand water loss from boiling was corrected.

Solution B was poured into a 2 liter stainless steel autoclave. SolutionA was added to the autoclave. Rinse Water was used to rinse the beakerand added to the autoclave. The contents of the autoclave were mixeduntil a smooth gel was obtained. The gel had the following compositionexpressed in moles of pure oxide:

    2.61 K.sub.2 O/1.0 Al.sub.2 O.sub.3 /10SiO.sub.2 /158 H.sub.2 O

The filled autoclave was pressurized to 65 psig with nitrogen gas andthen heated in 48 hours to a wall temperature of 79° C. withoutstirring. The autoclave was then stirred at 20 rpm and heated to a walltemperature of 150° C. in 56 hours. Stirring was stopped and theautoclave was maintained at 150° C. for 56 hours.

The product was removed from the autoclave and washed 3 times with colddemineralized water. The pH of the first wash was 12.3, the Ph of thesecond wash was 11.7 and the pH of the final wash 11.4. The product wasdried over night at 150° C. The amount of product recovered was 310grams. X ray diffraction analysis showed the dried product was purezeolite KL.

A portion of the calcined product was formed into silica bound 2 mmextrudates as follows:

    ______________________________________                                        Components Used          Quantity                                             for Preparation          (Grams)                                              ______________________________________                                        Silica Sol (Nalcoag 1034A) Zeolite KL Crystals                                                         124.68                                               Silica H.sub.2 O Gel (Aerosil 200) Water                                                               11.91                                                H.sub.2 PtCl.sub.6.6H.sub.2 O                                                                          2.92                                                 H.sub.2 O                26.28                                                Rinse H.sub.2 O          9.72                                                 Aluminosilicate LTL crystals (KL)                                                                      126.2                                                Additional H.sub.2 O     3.0                                                  Methocel (Hydroxypropyl methyl cellulose                                                               0.87                                                 extrusion Acid)                                                               ______________________________________                                    

The above components were mixed in a household mixed in the order shown.After adding the methocel, a thickened and extrudable dough wasobtained. The total mixing time was about 30 minutes.

The dough was extruded into 2 mm extrudates, dried for 2 hours at roomtemperature and then for 16 hours at 120° C., broken into 5mm pieces andthen calcined at 490° C. for 5 hours in air. The amount of calcinedproduct recovered was 139.3 grams.

Composition of calcined silica-bound extrudates:

Zeolite KL: 69.5 wt. %

SiO₂ Binder: 29.9 wt. %

Platinum: 0.6 wt %

The silica-bound zeolite KL extrudates were converted into zeolite KLbound by zeolite KL as follows:

A potassium aluminate solution was prepared from the following (weightof the chemicals in grams):

KOH pellets, purity 87.3%=8.44

Al(OH)₃ powder, purity 98.5%=6.40

H₂ O=56.65

The alumina was dissolved by boiling until a clear solution wasobtained. The solution was cooled to room temperature and corrected forwater loss due to boiling. The aluminate solution was quantitativelytransferred with 5.92 grams of rinse water into a 300 ml stainless steelautoclave. Next 50.00 grams of silica-bound extrudates containing 29.9wt. % of silica binder (0.20 grams of adsorbed water in extrudates) wereadded to the contents of the autoclave. The extrudates had beenpreviously dried to remove adsorbed water. The composition of themixture in the autoclave, corrected for the water content of theextrudates, was:

    2.64K.sub.2 O/1.62Al.sub.2 O.sub.3 /10SiO.sub.2 /148H.sub.2 O

In this mixture the silica is present as the binder in the extrudate.

The autoclave was heated up to 175° C. within 4.5 hours and kept at thistemperature for 65 hours. After this aging period the autoclave wasopened and the product-extrudates were collected.

The extrudates were washed two times with 500 ml of water (temperature60° C.) and then washed with 250 ml of water (temperature 60° C.). ThepH of the final wash water was 10.8 and the conductivity was 321 μS/cm.The extrudates were dried over night at 120° C. The amount of productrecovered was 55.8 grams.

The product-extrudates were characterized by XRD and SEM with thefollowing results:

XRD: Indicated the presence of zeolite L

SEM: Showed presence of zeolite L crystals bound by newly formed smallercrystals

II. Catalyst D--Platinum Loaded by Pore Filling

A portion of the calcined LTL structure type aluminosilicate (zeoliteKL) used to prepare Catalyst C was formed into silica bound 2 mmextrudates as follows:

    ______________________________________                                        Components Used        Quantity                                               for Preparation        (Grams)                                                ______________________________________                                        Silica Sol (Nalcoag 1034A)                                                                           128.2                                                  Silica H.sub.2 O Gel (Aerosil 200)                                                                   12.26                                                  Water                  37.06                                                  Zeolite KL Crystals    130.01                                                 Methocel (Hydroxypropyl methyl cellulose                                                             0.88                                                   extrusion Acid)                                                               ______________________________________                                    

The above components were mixed in a household mixed in the order shown.After adding the methocel, a thickened and extrudable dough wasobtained. The total mixing time was about 18 minutes.

The dough was extruded into 2 mm extrudates, dried for 2 hours at roomtemperature and then for 16 hours at 120° C., broken into 5 mm piecesand then calcined at 490° C. for 5 hours in air. The amount of calcinedproduct recovered was 147.39 grams.

Composition of silica-bound extrudates:

Zeolite KL: 69.95 wt. %

SiO₂ Binder: 30.05 wt. %

The silica-bound zeolite KL extrudates were converted into zeolite KLbound by zeolite KL as follows:

A potassium aluminate solution was prepared from a potassium aluminatesolution was prepared from the following (weight of the chemicals ingrams):

KOH pellets, purity 87.3%=9.25

Al(OH)₃ powder, purity 98.5%=6.43

H₂ O=56.99

The alumina was dissolved by boiling until a clear solution wasobtained. The solution was cooled to room temperature and corrected forwater loss due to boiling. The aluminate solution was quantitativelytransferred with 5.94 grams of rinse water into a 300 ml stainless steelautoclave. Next 50.0 grams of the silica-bound extrudates containing 30wt. % of silica binder (0.47 grams of adsorbed water in extrudates) wereadded to the contents of the autoclave. The extrudates had beenpreviously dried to remove adsorbed water. The composition of themixture in the autoclave, corrected for the water content of theextrudates, was:

    2.88K.sub.2 O/1.62Al.sub.2 O.sub.3 /10SiO.sub.2 /148H.sub.2 O

In this mixture the silica is present as the binder in the extrudate.

The autoclave was heated up to 175° C. within 5.5 hours and kept at thistemperature for 65 hours. After this aging period the autoclave wasopened and the product-extrudates were collected.

The extrudates were washed with 2000 ml of water for 1 hour (temperature60° C.) and then washed with 1000 ml of water for 2 hours (temperature60° C.). The pH of the final wash water was 10.8 and the conductivitywas 662 μS/cm. The extrudates were dried over night at 120° C. Theamount of product recorded was 52.6 grams.

The product-extrudates were characterized by XRD and SEM with thefollowing results:

XRD: Indicated the presence of zeolite L

SEM: Showed presence of zeolite L crystals bound by newly formed smallercrystals

An amount of 0.85 wt. % of platinum (based on the weight of catalyst)was loaded into Catalyst D by the pore-filling method with anappropriate amount of Pt (NH₃)₄ Cl₂ dissolved in water. After loading,the catalyst was dried.

EXAMPLE 4

Two separate aromatization tests were carried out using Catalyst C andCatalyst D. Prior to start of the tests, each catalyst underwent aredispersion procedure and a reduction procedure as follows:

10 grams of catalyst was loaded in a one inch ID quartz tube that wasplaced in an electrically heated oven. For all of the treatment stepsdescribed gas flowed through the tube and catalyst sample at a flow rateof 500 cc/minute. The catalyst was initially heated to 450° C. with agas composition of 10 volume percent O₂ and 90 volume percent helium.The catalyst was held at 450° C. for one hour. The temperature was thenincreased to 530° C. and the gas composition changed to 20 volumepercent O₂, 2.2 volume percent H₂ O, and 77.8 volume percent helium. Thecatalyst was exposed to these conditions for 67.5 hours. The catalystwas then cooled to 510° C. in dry helium. At that point, the gascomposition was changed to 20 volume percent O₂, 2.2 volume percent H₂O, and 77.8 volume percent helium. After 30 minutes the gas compositionwas changed to 0.8 volume percent chlorine, 20 volume percent O₂, 2.2volume percent H₂ O and 77.0 volume percent helium. The catalyst wasexposed to these conditions for 2 hours. The gas composition was thenchanged to 20 volume percent O₂, 2.2 volume percent H₂ O and 77.8 volumepercent helium. After two hours at these conditions the O₂ was removedand residual oxygen purged from the reactor with 2.2 volume percent H₂ Oand 97.8 volume percent helium. At that point, hydrogen was introducedto change the gas composition to 20 volume percent H₂, 2.2 volumepercent H₂ O and 77.8 volume percent helium. The catalyst was reduced atthese conditions for one hour. The gas composition was then changed todry helium and the catalyst cooled to room temperature and removed fromthe reactor.

The first aromatization test was carried out at a temperature of 950° F.and 1000 psig pressure with a C₆ mixed feed comprising 60% by weight andn-hexane, 30% by weight 3-methylpentane, and 10% by weightmethylcyclopentene, at a weight hourly space velocity of 6.0 w/w hr⁻¹and in the presence of hydrogen, the H₂ :hydrocarbon ratio being 6. Thetime on stream for Catalyst C was 14.6 hours and Catalyst D was 14.4hours. The results are set forth in Table 3 below:

                  TABLE 3                                                         ______________________________________                                        Product       Catalyst C                                                                             Catalyst D                                             ______________________________________                                        C.sub.1 -C.sub.2                                                                            5.8      13.5                                                   C.sub.3 -C.sub.4                                                                            6.6      16.6                                                   C.sub.5 -C.sub.6                                                                            21.3     11.0                                                   Benzene       66.3     58.4                                                   Toluene       0.1      0.3                                                    A.sub.8.sup.+ 0.0      0.1                                                    ______________________________________                                    

The data in the Table shows that Catalyst C had 14 percent higherbenzene yield than Catalyst D and had more than 50% less undesirablefeed stream cracking to C₁ -C₄ products.

The second aromatization test was carried out at a temperature of 860°F. and a 100 psig pressure with a light virgin naphtha feed at a weighthourly space velocity of 1.0 w/w hr 1 and in the presence of hydrogen,the H₂ :hydrocarbon ration being 6. The time on stream for Catalyst Cwas 16.5 hours and Catalyst D was 16.3 hours. The composition of the LVNfeed comprised:

    ______________________________________                                        Component     Weight %                                                        ______________________________________                                        C.sub.5       0.26                                                            C.sub.6       5.85                                                            C.sub.7       18.99                                                           C.sub.8       22.35                                                           C.sub.9       21.60                                                           C.sub.10      10.37                                                           C.sub.11      2.93                                                            Benzene       0.32                                                            Toluene       3.13                                                            A.sub.8       5.33                                                            A.sub.9       8.07                                                            A.sub.10      0.80                                                            ______________________________________                                    

The results of these tests are set forth below in Table 4.

                  TABLE 4                                                         ______________________________________                                        Product       Catalyst C                                                                             Catalyst D                                             ______________________________________                                        C.sub.1 -C.sub.2                                                                            7.2      12.0                                                   C.sub.3 -C.sub.4                                                                            3.3      3.7                                                    C.sub.5 -C.sub.6                                                                            30.9     20.5                                                   Benzene       10.0     14.3                                                   Toluene       22.1     31.5                                                   A.sub.8       20.0     15.1                                                   A.sub.9       5.8      2.6                                                    A.sub.10      0.6      0.3                                                    ______________________________________                                    

The data in the Table shows that Catalyst C had over 50 percent greaternet A₈ yield than Catalyst D and also had more than 40% reduction infeed stream cracking to C₁ -C₂. Catalyst D produced more benzene andtoluene than Catalyst C but partially at the expense of more desirablexylenes.

What is claimed is:
 1. A zeolite bound zeolite hydrocarbon conversioncatalyst which does not contain significant amounts of non-zeoliticbinder and contains at least one hydrogenation/dehydrogenation metal andcomprises:(a) first crystals of a first zeolite, and (b) a bindercomprising second crystals of a second zeolite; and (c) an effectiveamount of at least one hydrogenation/dehydrogenation metal:wherein saidzeolite bound zeolite catalyst is prepared by (i) providing said firstcrystals of said first zeolite; (ii) forming a silica bound aggregatecomprising at least a portion of said at least onehydrogenation/dehydrogenation metal and said first crystals of saidfirst zeolite; and (iii) converting to said second zeolite the silicabinder of said silica bound aggregate, wherein said portion of said atleast one hydrogenation/dehydrogenation metal is added during thepreparation of said zeolite bound zeolite hydrocarbon conversioncatalyst after step (i).
 2. The catalyst recited in claim 1, whereinsaid second crystals are intergrown and form at least a partial coatingon said first crystals.
 3. The catalyst recited in claim 2, wherein saidfirst crystals of said first zeolite have an average particle sizegreater than about 0.1 micron and said second crystals of said secondzeolite have an average particle size that is less than said firstcrystals of said first zeolite.
 4. The catalyst recited in claim 3,wherein said first zeolite is a structure type selected from the groupconsisting of OFF, BEA, MAZ, MEI, FAU EMT, LTL, VFI, MOR, MFI, MFS, MEL,MTW, MTT, FER, EUO, HEU, TON, CHA, ERI, KFI, LEV, and LTA.
 5. Thecatalyst recited in claim 4, wherein said second zeolite is a structuretype selected from the group consisting of OFF, BEA, MAZ, MEI, FAU, EMT,LTL, VFI, MOR, MFI, MFS, MEL, MTW, MTT, FER, EUO, HEU, TON, CHA, ERI,KFI, LEV, and LTA.
 6. The catalyst recited in claim 5, wherein saidfirst zeolite and said second zeolite are an aluminosilicate zeolite ora gallium silicate zeolite.
 7. The catalyst recited in claim 6, whereinsaid second zeolite has lower acidity than said first zeolite.
 8. Thecatalyst recited in claim 7, wherein said second crystals are resistantto attrition.
 9. The catalyst recited in claim 6, wherein the acidity ofsaid second zeolite is higher that the acidity of said first zeolite.10. The catalyst recited in claim 6, wherein said first zeolite and saidsecond zeolite have a large pore size or an intermediate pore size. 11.The catalyst recited in claim 6, wherein said first zeolite has a silicato alumina mole ratio of from about 70:1 to about 700:1 or a silica togallia mole ratio from about 24:1 to about 500:1.
 12. The catalystrecited in claim 11, wherein the average particle size of the crystalsof said first zeolite is from about 1 to about 6 microns and the averageparticle size of the crystals of said second zeolite is from about 0.1to about 0.5. microns.
 13. The catalyst recited in claim 6, wherein saidcatalyst is prepared by aging at elevated temperatures a silica-boundaggregate containing said hydrogenation/dehydrogenation metal and firstcrystals of said first zeolite in an aqueous ionic solution containing asource of hydroxy ions sufficient to convert the silica binder to thesecond zeolite.
 14. The catalyst recited in claim 13, wherein saidzeolite bound zeolite catalyst contains less than 5% by weight ofnon-zeolitic binder based on weight of said first zeolite and saidsecond zeolite.
 15. The catalyst recited in claim 6, wherein said firstzeolite and said second zeolite have LTL structure type.
 16. Thecatalyst recited in claim 6, wherein said first zeolite and said secondzeolite have a MFI or MEL structure.
 17. The catalyst recited in claim16, wherein said first zeolite has a silica to aluminum mole ratio from70 to 700 or a silica to gallia mole ratio from 20 to
 500. 18. Thecatalyst recited in claim 17, wherein said second zeolite has a silicato alumina mole ratio greater than 200 or a silica to gallia mole ratiogreater than
 100. 19. The catalyst recited in claim 6, wherein said atleast hydrogenation/dehydrogenation metal comprises a Group VIIIA metal.20. A process of preparing a hydrogenation/dehydrogenation metalcontaining-zeolite bound zeolite catalyst which does not containsignificant amounts of non-zeolitic binder and contains first crystalsof a first zeolite, a binder comprising second crystals of a secondzeolite, and said hydrogenation/dehydrogenation metal, said processcomprising:(i) providing said first crystals of said first zeolite; (ii)forming a silica bound aggregate comprising at least a portion of saidat least one hydrogenation/dehydrogenation metal and said first crystalsof said first zeolite; and, (iii) converting to said second zeolite thesilica binder of said silica bound aggregate,wherein said portion ofsaid at least one hydrogenation/dehydrogenation metal is added duringthe preparation of said zeolite bound zeolite catalyst after step (i).21. The process recited in claim 20, wherein said at least onehydrogenation/dehydrogenation metal is a Group VIIIA metal.
 22. Theprocess recited in claim 21, wherein said crystals are intergrown andform at least a partial coating on said first crystals.
 23. The processrecited in claim 22, wherein said first crystals of said first zeolitehave an average particle size greater than about 0.1 micron and saidsecond crystals of said second zeolite have an average particle sizethat is less than said first crystals of said first zeolite.
 24. Theprocess recited in claim 23, wherein said first zeolite is a structuretype selected from the group consisting, of OFF, BEA, MAZ, MEI, FAU EMT,LTL, VFI, MOR, MFI, MFS, MEL, MTW, MTT, FER, EUO, HEU, TON, CHA, ERI,KFI, LEV, and LTA.
 25. The process recited in claim 24, wherein saidsecond zeolite is a structure type selected from the group consisting ofOFF, BEA, MAZ, MEI, FAU, EMT, LTL, VFI, MOR, MFI, MFS, MEL, MTW, MTT,FER, EUO, HEU, TON, CHA, ERI, KFI, LEV, and LTA.
 26. The catalystrecited in claim 25, wherein said first zeolite and said second zeoliteare an aluminosilicate zeolite or a gallium silicate zeolite.
 27. Theprocess recited in claim 26, wherein said silica bound aggregate isprepared by forming an extrudable mass containing said silica and saidfirst crystals of said zeolite, extruding said extrudable mass to forman extrudate, and calcining the extrudate.
 28. The process recited inclaim 27, wherein said silica bound aggregate is prepared by forming anextrudate mass which contains said metal, said silica and said firstcrystals of said first zeolite and extrudating said mass.
 29. Theprocess recited in claim 28, wherein said catalyst is prepared by agingat elevated temperatures a silica-bound aggregate containing saidhydrogenation/dehydrogenation metal and first crystals of said firstzeolite in an aqueous ionic solution containing a source of hydroxy ionssufficient to convert the silica binder to the second zeolite.
 30. Theprocess recited in claim 29, wherein said hydrogenation/dehydrogenationmetal is added to said aqueous solution.
 31. The process recited inclaim 30, wherein said first zeolite and said second zeolite have LTLstructure type.
 32. The process recited in claim 31, wherein said firstzeolite and said second zeolite have a MFI or MEL structure type. 33.The process recited in claim 32, wherein said zeolite bound zeolitecatalyst contains less than 5% by weight of non-zeolitic binder based onweight of said first zeolite and said second zeolite.
 34. The processrecited in claim 33, wherein said at least hydrogenation/dehydrogenationmetal comprises a noble metal.
 35. The process recited in claim 34,wherein said first zeolite has a silica to alumina mole ratio from 70 to700 or a silica to gallia mole ratio from 20 to
 500. 36. The processrecited in claim 35, wherein said second zeolite has a silica to aluminamole ratio greater than 200 or a silica to gallia mole ratio greaterthan
 100. 37. The process recited in claim 28, whereinhydrogenation/dehydrogenation metal is incorporated into said extrudateprior to calcining.
 38. The process recite in claim 37 wherein saidhydrogenation metal/dehydrogenation metal is incorporated into saidextrudable mass by physical mixing.
 39. The process recited in claim 38,wherein said second zeolite has lower acidity than said first zeolite.40. The process recited in claim 28, wherein saidhydrogenation/dehydrogenation metal is present in said catalyst in anamount of from about 0.05 to about 3.0 wt. percent.
 41. The processrecited in claim 40, wherein said hydrogenation/dehydrogenation metal isincorporated into extrudate after said calcining of said extrudate.